NEWS & PRESS

Astronomers from the Scottish Universities Physics Alliance (SUPA) have produced a completely new catalogue of ~15,000 groups of galaxies that gives a new insight into dark matter, the material of unknown composition that makes up a fifth of the mass of the Universe. Dr Aaron Robotham of the University of St Andrews will present the work of the Galaxy and Mass Assembly (GAMA) team in his talk on Thursday 21 April at the Royal Astronomical Society's National Astronomy Meeting in Llandudno, Wales.

Current models of the Universe predict that galaxies reside in large clumps of dark matter, commonly referred to as dark matter halos. Unlike individual galaxies, galaxy groups provide a unique environment in which to study the properties of this elusive material. Understanding the 20% of the cosmos comprised of dark matter is important – in comparison only 3% of the mass of Universe consists of 'ordinary' matter.

Part of an image of a galaxy cluster discovered in the GAMA group catalogue. This is a inverse colour composite of ultraviolet, visible light and infrared images so redder galaxies appear blue and vice-versa. Galaxies in the cluster are highlighted with circles, with the size of the circle proportional to the mass of the galaxy. The colour of the circle indicates the true colour of the galaxy. In this image a mixture of galaxy types are visible, but very few blue (star-forming) galaxies. The brightest galaxy is located at the centre. Credit: GAMA / Aaron Robotham

"The motions of the galaxies inside the groups provide a direct method for studying the properties of dark matter", says Dr Aaron Robotham who leads the group catalogue project. "Studying dark matter in galaxies is confused by normal processes such as star formation, while this unseen material dominates the motions of galaxies in groups".

Dr Robotham describes the construction of the group catalogue, which is a significant improvement on previous similar attempts with much shallower surveys. "The sample has some of the most massive bound structures ever measured. These range from the equivalent of a million billion times the mass of the Sun down to a mere few thousand billion solar masses. To have this range of dark matter halo masses within a single study is unprecedented".

"Some of our groups contain hundreds of galaxies while others only a handful", says Dr Peder Norberg, a co-investigator based at the Royal Observatory Edinburgh, "the ratio of the number of very high mass to very low mass groups is a direct indicator of the type of dark matter that the Universe contains. Hot or warm dark matter (meaning light particles) suppresses the formation of low mass halos while cold dark matter (heavy particles) encourages their formation."

It will take a further few years of detailed studies, with a large range of models, before a definite conclusion can be reached on whether the new GAMA data and supercomputer predictions (based on the popular Cold Dark Matter model of the Universe) are in good agreement or not.

"Currently the differences seen between the model and the data can be understood as limitations in the galaxy formation model used, explaining why intense modelling and further studies are required, and hopefully leading to some exciting new findings in the years ahead with possibly the first new insight into the properties of dark matter particles," adds Dr. Norberg.

GAMA team leader Professor Simon Driver of the University of St Andrews and the International Centre for Radio Astronomy Research at the University of Western Australia, says this group catalogue is the first big step of 4 years of data gathering by the GAMA Team at the Anglo-Australian Telescope. "The catalogue will provide the opportunity to study how gravity works over an unprecedented mass range and using data from other telescopes around the world we will shed fresh light on how dark mater helps to turn gas into stars".

In Australia (Perth, GMT+8hrs)Prof Simon DriverGAMA Team leaderInternational Centre for Radio Astronomy Research (ICRAR)University of Western AustraliaTel: +61 8 6488 7747Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

The GAMA survey is major international collaboration which will eventually combine the data flows from five ground-based telescopes, three space-missions, and two radio arrays. The survey will eventually cover six large patches of sky and provide multi-wavelength measurements for almost 400,000 galaxies from X-ray thru UV, optical and IR to Radio wavelengths. The construction of the group catalogue is a major milestone for the team and follows the first data release last year. More information on the survey is available from the GAMA website: http://www.gama-survey.org/

The Royal Astronomical Society (RAS: http://www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The Science and Technology Facilities Council

The Science and Technology Facilities Council (STFC: http://www.stfc.ac.uk) ensures the UK retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innovative technologies; and increasing the socio-economic impact of its research through effective knowledge exchange. The Council has a broad science portfolio including Astronomy, Particle Astrophysics and Space Science. In the area of astronomy it funds the UK membership of international bodies such as the European Southern Observatory.

Venue Cymru

Venue Cymru (http://www.venuecymru.co.uk) is a purpose built conference centre and theatre with modern facilities for up to 2000 delegates. Located on the Llandudno promenade with stunning sea and mountain views; Venue Cymru comprises a stunning location, outstanding quality and exceptional value: the perfect conference package.